The objective of this project is to study the pathogenesis of rabbit coronavirus (RbCV), the rabbit's physiologic response to this virus, and the relatedness of RbCV to other members of the Coronaviridae. Pleural effusion disease (PED) virus and RbCV have been shown to induce similar clinical signs and lesions. Each virus induces antibody which partially neutralizes both viruses. Blood from rabbits given RbCV exhibited decreased platelet counts, RBCs, hematocrits, and hemoglobin levels. Leukopenia followed by leukocytosis with a left shift was seen. Serum creatine kinase (CK) levels increased as much as 217 times pre-inoculation levels on day 4 post infection. With the elevated CK, lipemia was common. Prothrombin time increased from 9.1 seconds to greater than 150 seconds 4 days following infection. Assessment of myocardial damage using ECGs and creatine kinase isozymes are beginning. Likewise, further examination of coagulation factors, activated partial thromboplastin time, prothrombin time, thrombin time and fibrinogen levels are planned. Antibodies to other coronaviruses are being produced for use in studying the relatedness of RbCV to other Coronaviridae. The significance of this work lies in the ability to study a viral disease with a cardiotropism in an animal of sufficient but manageable size to allow sequential clinical and physiological observations. The damage to the rabbit heart by RbCV has a corollary in the human heart with the Coxsackie viruses, Mycoplasma pneumoniae, influenza virus, Herpes zoster, and possibly other infectious agents.